Optical fiber splicing involves joining two optical fibers together, which is typically accomplished either by employing a fusion splicer or a mechanical splicer, each a different type of instrument. The fusion splicer results in more reliable low loss splicing (<0.1 dB) than the mechanical splicer, but has the significant drawbacks of being very expensive, bulky and fragile and not suitable for field use. The current mechanical splicers require only a few hand tools, are portable and take up very little space, but their splicing performance is not only inferior (˜0.3 dB) but also erratic due to their design. The currently available mechanical splicers, which all aim to splice optics fibers by aligning the fibers butt to butt and coupling them together, are difficult to operate and/or produce unpredictable results. The present invention provides a precision aperture mechanical splicer that addresses these shortcomings of the prior arts of mechanical splicers.
The present invention discloses a precision aperture mechanical splicer housed within a sleeve of precise diameter, that produces simple, inexpensive, reliable and stable mechanical splicing, and whose performance meets stringent optical coupling low insertion loss requirements. It designates a method for mechanical splicing that matches the performance of fusion splicers but that is much more economical and practical for field use. To illustrate the economic value of the present invention, skilled operators in the art will appreciate that, whereas a fusion splicer costs upwards of US$20K and is unwieldy and difficult for use in the field, the present invention utilizes parts that in total cost less than US$2K in the present industry. Also presented here is a pre-polished fiber optical connector that is particularly applicable for field use, including a built-in precision aperture mechanical splicer as per this invention. Also presented is a fiber holder with a precision aperture that relates the precision sleeve housing as the mechanical datum for fiber alignment.
The mechanical splicing of two optical fibers butted against each other aims to join two fibers with minimal optical power loss (e.g. insertion loss, or IL). Such low loss coupling must meet the following stringent physical requirements:                a) Two fiber stubs aligned center to center, i.e. no radial offset.        b) Two fiber stubs aligned perfectly parallel, i.e. no angular offset        c) Two flat ends of fiber studs spliced with seamless contact and no gaps, i.e. no lateral offset.        
The coupling of two optical fiber studs can be stable and have high reliability if                d) The connection structure is mechanically stable under a full range of operation environments, such as high/low temperatures, and can endure shock and vibration.        
Achieving all four conditions simultaneously is highly difficult, due to the fact that each fiber stud is typically less than the width of a human hair, and even minimal offsets in alignment can result in significant optical power loss. In the case of single mode fiber optics, 0.3 dB IL or less is acceptable according to industry standards. All prior arts known were attempting to resolve these issues.
There have been many patents issued relating to the art of optical fiber mechanical splicing and connecting.
U.S. Pat. No. 3,989,567 by Tardy, U.S. Pat. No. 4,123,139 by Sandahl, U.S. Pat. No. 4,047,796 by Kao et al, U.S. Pat. No. 4,223,976 by Zangiacomi et al, U.S. Pat. No. 4,490,007 by Murata, and U.S. Pat. No. 5,351,371 by DeVeau, Jr. et al., were all attempting to solve mechanical splicing problems by utilizing a 3-rod bundle in order to form a straight aperture into which the two fiber studs would be inserted and aligned butt to butt.
Prior arts such as U.S. Pat. No. 4,123,139, by Sandahl and U.S. Pat. No. 4,047,796, by Kao prescribed the use of a bundle of 3 rods of equal size, with a very precise mechanical tolerance. Using planar geometry, these prior arts could calculate a precise aperture formed by the 3 equally-sized rods. However, these prior arts' high requirements for the mechanical tolerance of the rods present a significant problem—U.S. Pat. No. 4,123,139, by Sandahl specifies rod mechanical tolerance to be +/−0.00001″ and U.S. Pat. No. 4,047,796, by Kao specifies rods mechanical tolerance to be +/−0.0001″. All these prior arts' precise rod size calculations are based on the requirement that the three rods be of equal size, but per the state of current technology, such rods are at this time highly expensive, with their cost of production so high as to make their use very impractical. Furthermore, there is yet another difficulty presented by these prior arts. In the case that the rod size tolerance is specified to be +/−0.0001″, it is still likely that the fiber will be difficult to insert into the aperture, as will be described hereinafter. Thus, these prior arts resort to using a loose rod bundle into which the fibers are inserted. This is then followed by a clamping mechanism that wraps around the rod bundle and binds the rods and fibers in the hopes that the splicing fibers will still butt against each other without losing their alignment or breaking. However, the performance of such splicers is not predictable and thus results in much wasted time and materials. These issues are well known to operators skilled in the art. Despite the existence of these patents for over 20 years, the current commercially available mechanical splicers do not use these prior arts or the method of a 3-rod bundle, except for fiber guiding. However, the present invention eliminates the need for rods with high mechanical tolerance and also eliminates the need for a clamping mechanism.
U.S. Pat. No. 4,676,589, by Miyashta, et al., attempts to solve the challenge of splicing optical fibers by using a mechanical splicer consisting of an undersized U or V-shaped groove and a semi-circular plastic insert wrapped around by a sleeve. The design is simple but does not work well, because it is difficult to manufacture a V or U groove precise enough to accommodate the extremely fine width of an optical fiber. The V or U aperture is most often either too small, thus causing the optical fiber to be difficult to insert and resulting in fiber breakage, or the grooves are too loose, thus causing too much optical insertion loss (IL).
There also exist prior mechanical splicers involving the creation of very precise through-holes, as described in U.S. Pat. No. 6,981,802B2, by Sasaki, et al. and U.S. Pat. No. 6,779,931B2 by Murata, et al. However, these splicers are extremely difficult to fabricate because it is difficult to fabricate a long, straight and precise through-bore-hole with a diameter not much larger than the size of a human hair. In addition, this type of splicer requires either an extra vent hole or a special transfer procedure in order to avoid the air piston effect that would prevent the fiber stud end-faces from butting against each other.
Due to the difficulty and imperfect nature of the precision V groove or bore hole prior splicers, there were many more attempts to solve this problem without requiring a precise V groove or through-bore-hole, such as that described in U.S. Pat. No. 4,921,323, by Delahanty et al. In essence, Delahanty and others utilized a V or U groove as the optics fiber alignment feature, along with an insert and a flat surface that were separated or loosely assembled before fiber insertion in order to facilitate the ease of fiber insertion. Once both optics fibers were inserted and butted against each other, the designs then involved either complex mechanical structures, or special polymer materials used to activate and force the optics fibers against the alignment feature. However, it is difficult to achieve reliable and repeatable splicing with such designs due to the complex mechanical structure that often causes the clamp force to apply unevenly or inconsistently, thus ending in unpredictable splicing results after clamping. The V or U groove method remains the most commonly used method of mechanical splicing in the industry today. However, operators skilled in the art are familiar with the difficulties that such splicers present, as multiple try and re-try of the splicing operation, check and double check of the splicing insertion loss are needed in order to reach satisfactory results.
The present invention also solves the difficulties involved in preparing fiber optic connectors in order to terminate fiber optic cables during field work. Such difficulties are well known. Terminating optical fibers with connectors requires skilled labor, expensive polishing equipment, consumable materials, and working space. Also required are time-consuming epoxy mixing and curing, and a tricky connector polishing process. Considering cost, time and skilled labor, it is not practical to polish a connector in the field, thus making a pre-polished connector an invaluable field component. Therefore, combining a pre-polished connector with a built-in mechanical splicer to splice the connector with a field optical fiber, so it can be terminated with the connector easily and quickly—all without a fusion splicer and a connector pigtail or connector polishing—would be highly efficient and desirable for field optics fiber installation. It would allow a field operator to restore or establish an optics connection within a few minutes.
Prior arts have sought to address this need. U.S. Pat. No. 4,743,084 by Manning et al, U.S. Pat. No. 6,179,482 B1 by Takizawa et al., U.S. Pat. No. 7,011,454, by Caveney et al, and U.S. Pat. No. 7,264,410 by Doss, et al. all attempt to incorporate a mechanical splicer with a pre-polished fiber stud connector. In order to facilitate the easy insertion of a field optics fiber, these patents either utilize “shape memory” material with radial deformable means, or a V or U groove plank and a flat surface plank in either an open or loose position. Again, after the field fiber is inserted, a clamping feature is always needed, supplied by crimping or by triggering a cam mechanism, or by removing a pry member to push a flat plank, which forces both fibers studs against alignment features. Such inventions all suffer from similar shortcomings of a complex mechanical structure. Their erratic splicing performance does not compete well with fusion splicing methods, unless used for emergency connection restoration or for applications for which optical performance is not so demanding. However, the present invention remedies these difficulties by utilizing a precision aperture mechanical splicer with a pre-polished connector. With the present invention, consistent, stable and low IL (insertion loss) performance can be expected due to its simplicity and precision, lack of clamping and actuating mechanisms, and durable mechanical structure.
The present invention also has applicability to the holding of optical fibers in any number of processes that require optical fibers to be held steadily and/or guided. The current bare optics fiber holders used to facilitate accurate fiber optics sensing or processing consist of V- or U-shaped features for fiber guiding and clamping. U.S. Pat. No. 6,741,786, by Flower et al attempts to resolve a problem common to current fiber holders that apply too much stress on the optical fiber during fiber guiding and clamping, which can result in undesirable bends or deformation of the fiber. Flower describes ways to interleave fiber guiding and holding in order to minimize the stress and bending deformation of the fiber. The present invention further improves upon the optics fiber holding methods of Flower by providing strain-less fiber guiding and involves only evenly localized Hook stress applied to the fiber outside buffer. With the present invention, the fiber position may also be easily aligned with reference datum, such as a sleeve that contains a rod bundle, for sensing and further processes. This invention can be applied to any fiber optics devices that also require optical fibers to be held precisely and steadily.